Almost degenerate neutrinos

Abstract

The three experimental findings namely, deficits in the solar and atmospheric neutrino fluxes and the need for a significant hot component in the dark matter can be simultaneously reconciled with three light neutrinos only if they are almost degenerate. A scenario proposed to understand this degeneracy and small departures from it is discussed. Small differences in the neutrino masses arise in this scenario due to non-zero up-quark or charged lepton masses. These are such that the hierarchy required for the simultaneous solution of the solar and atmospheric neutrino problem is correctly reproduced. Moreover, the common mass scale for the neutrino is fixed to be in the eV range as required for the solution to the dark matter problem if one identifies the majorana masses of the right handed neutrinos with the grand unification scale. Possible models leading to a realization of this scenario are discussed.